expression
Used to introduce a simplified summary or rephrasing of a previous statement. Common in both spoken and written Japanese.
簡単に言えば、この計画は失敗だった。
Simply put, this plan was a failure.
彼の説明は長かったが、簡単に言えば「ノー」ということだ。
His explanation was long, but in short, it means 'no'.
A very common conjunction meaning 'in other words' or 'that is to say'. 簡単に言えば explicitly highlights that the following statement is a simplified version.
A set phrase composed of 簡単に (simply) + 言えば (conditional form of 言う, 'to say'), literally 'if one says it simply'.